Association of ankylosing spondylitis with HLA-B27 and ERAP1: pathogenic role of antigenic peptide.

Ankylosing spondylitis (AS) is a form of seronegative inflammatory arthritis whose strong genetic association with the human leucocyte antigen (HLA)-B27 has been known for almost 4 decades. However, its mechanism remains poorly understood. Recently, with the development of genetics, further more genes have been robustly associated with the disease. Genome-wide association studies identified the association between AS and ERAP1 (endoplasmic reticulum associated aminopeptidase 1). And ERAP1 has shown the potential in trimming antigenic peptides to optimal length for binding to HLA-B27 in the ER (endoplasmic reticulum). However, the length of the peptides are strictly restricted in the process of peptide transporting, processing and presentation. A hypothesis is proposed that the abnormal mechanism of AS may related to the trimming of N-terminal sequences from antigenic precursors in the ER and the length of the antigenic peptides that are presented to the T-cell receptors.